1. Technical Field of the Invention
This disclosure relates to an electrophotographic photoconductor containing a specific disazo pigment serving as a charge generation agent, a specific triphenylamine compound serving as a charge transport agent, and a binder resin, wherein the ratio of the charge transport agent to the binder resin falls within a suitable range.
2. Description of the Related Art
In recent years, long-wavelength light sources (e.g., laser diode and LED) are mostly used as an exposing source in non-impact printers employing electrophotography. In addition, with downsizing and speeding-up of copiers and printers, smaller photoconductors and high-speed processes have been employed. Thus, electrophotographic photoconductors generally include a charge generation agent sensitive to long-wavelength light. Conventionally, phthalocyanine pigments are often used as a material serving as such a charge generation agent. The phthalocyanine pigments are well known to exhibit different sensitivities depending on different crystal types. Furthermore, exposing sources used in electrophotographic apparatuses (e.g., printers) are required to be reduced in its power output for meeting the recent requirements (e.g., power saving). In view of this, keen demand has arisen for electrophotographic photoconductors with higher sensitivity.
Oxytitanium phthalocyanine is one of the phthalocyanine pigments highly sensitive to long-wavelength light of about 780 nm. In particular, oxytitanium phthalocyanine having a maximum diffraction peak of 27.2° is thought to be highly sensitive. When repeatedly used in a high-speed process, the photoconductor containing this oxytitanium phthalocyanine exhibits degraded potential characteristics, resulting in causing fogging, black streaks, density unevenness, etc. in the formed image. In a normal electrophotographic process, such high-sensitive oxytitanium phthalocyanine exhibits advantageous effects (e.g., highly sensitive responsiveness) since it generates a relatively large amount of charges; but in a high-speed electrophotographic process, excessive charges generated therefrom undesirably remain in the photosensitive layer to cause a memory residue on the photoconductor surface, resulting in that the memory residue is developed to form an unnecessary image at the subsequent electrophotographic processes. Furthermore, the charges are undesirably retained in the photosensitive layer under any working conditions (i.e., low-temperature, low-humidity conditions to high-temperature, high-humidity conditions). Recent interest has focused on an azo pigment sensitive to light with a wavelength of about 650 nm. The type thereof must be carefully determined in consideration of charge-transport performance of a charge transport agent used in combination (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2000-147807).
Under such circumstances, there has been demand for an electrophotographic photoconductor which is highly sensitive to long-wavelength light and which exhibits reliable electrophotographic characteristics even after repeatedly used (in particular, reliable chargeability at an initial state and after repetitive use). Meanwhile, even in use of a charge generation agent exhibiting high charge generation efficiency, when it is used together with a charge transport agent that is not effectively used in combination, the formed photoconductor cannot only exhibit sufficient sensitivity but also provide a high-quality image under any working conditions (i.e., low-temperature, low-humidity conditions to high-temperature, high-humidity conditions). Although studies have been carried out from various aspects on an effective combination of a charge generation agent and a charge transport agent, there is still room for research on it (see, for example, JP-A No. 60-175052).